JPS5819511A - Servo-type volume flowmeter - Google Patents

Abstract

PURPOSE:To measure a flow rate highly accurately by adding the values of pressure difference and temperature difference before and after rotors, the fluid pressure at the inflow side, and the like, and performing compensation. CONSTITUTION:The pressure difference at both ends of the servo type volume flowmeter 1 connected to a pipe 3 is detected by pressure difference detctors 12 and 17 through pipes 10 and 11. The output of the pressure difference detector 12 is inputted to a servomotor 7 which is connected to one rotor 2 in the flowmeter 1 through reduction gears 4 and 6 and a magnetic coupling 5. Thus the rotor 2 is driven so as not to cause the pressure difference. The output of the pressure difference detector 17 is inputted to a leaking amount compensating operator 18 which receives the output of a flow rate oscillator 16 that is connected to the other rotor 2 through a magnetic coupling 15 and gear trains 13 and 14. Since the flow rate value from the oscillator 16 is compensated by the operator 18 and the pressure difference detector 17 based on the temperature T1 and T2 before and after the rotors 2 and the value of an inflow side pressure gage PA, the true flow rate value can be counted with excellent accuracy.

Description

[Detailed description of the invention] The present invention relates to improvements in servo-type positive displacement flowmeters.

Generally, there is a small gap between the rotor and the inner chamber of a positive displacement flowmeter because they do not come into contact with each other, and each trochanter requires energy to rotate and generates a pressure difference. Therefore, leakage occurs from this gap.

Due to this leakage, the instrumental error characteristics of the positive displacement flowmeter become significantly negative in the small flow rate range, and are also affected by changes in fluid viscosity and density. By reducing this amount of leakage to zero, the small flow rate characteristics are improved, and the servo-made positive displacement flow rate needle embodies a high-precision flow needle that is unaffected by changes in fluid viscosity and density. needles are known. As shown in Figure 1, this system detects the pressure difference before and after the flowmeter, amplifies the differential pressure signal, and controls the rotor of the positive displacement flowmeter connected to the drive shaft of the servo motor to control the flow rate by driving the motor. It is a servo-type positive displacement flowmeter that is constructed so that the pressure difference before and after the meter is zero, and in principle there is no leakage. However, due to the characteristics of the servo control system, in reality, the pressure difference is completely zero. For example, it has been impossible to construct a stable and highly accurate servo-type positive displacement flow needle because it is impossible to control the pressure difference, typically a few millimeters of water column. If the system is controlled, the difference in pressure remaining before and after the rotor will increase as the error amplification characteristic increases, and even if the PI operation system is controlled, stability will increase. It is not possible to control the pressure difference to zero, and furthermore, if the pressure difference is to be controlled minutely, it not only requires a very complicated control system, but also makes its adjustment difficult, making it economically difficult. However, it also has disadvantages such as being expensive.

Further, the differential pressure needle, which is a detection part of the servo control system, is required to have stability such as zero point drift, and it is necessary to match the voltage output generated when the differential pressure is zero with the input voltage of the control system. For this reason, the rumored method of providing a dead zone in the control system or adjusting the zero output of the differential pressure detector is necessary, which is inconvenient for realizing more accurate measurement. for example,
When the pressure of the fluid increases slowly, a pressure difference larger than the normal control pressure difference may remain, or the average control difference may increase due to pulsation due to non-uniform rotation of the rotor. Since the pressures still show different values, it is impossible to actually control the pressure difference to zero. Also, the control system! When the Tsuchinda conditions are changed, the pressure difference to be controlled becomes different from the initially controlled pressure difference, the su weight changes, and there is a problem that the control system becomes unstable.

By the way, when we examine the relationship between the amount of leakage and the pressure difference before and after the flowmeter in a servo-type positive displacement flowmeter, we find that when the fluid is a gas, the amount of leakage is independent of the magnitude of the flow rate Q, as shown in Figure @2. It was found that ΔQ is proportional to the pressure difference ΔP. (In the case of liquids, it is necessary to take into account that the amount of leakage and viscosity are inversely proportional.) Therefore, even if the conventional sensor performs a correction to control the pressure difference to zero in a positive displacement flow needle, it will still be an error. remain. Therefore, by correcting the leakage amount corresponding to the residual pressure difference using the above relationship, it is possible to realize a servo type flowmeter with even higher viscosity. Furthermore, since ΔQ and ΔP have a linear relationship, a simple system configuration is possible in the servo control system.

This invention was developed by focusing on the points mentioned above, and first of all, it focuses on the ideal flow rate based on the gills measured by the measuring chamber, which is the original feature of positive displacement flowmeters. A servo-type volumetric system that implements measurement, is configured so that the amount of leakage between the rotor and the casing is proportional to the pressure difference before and after the rotor, and has a mechanism to measure the amount of leakage and calculate leakage amount correction. The second objective is to simplify the servo control system, make it easier to match the output from the differential pressure detector with the servo system, and to provide a servo control system that is a pressure reduction mechanism and a high-performance flowmeter. A servo-type positive displacement fstl with an independent system for the correction calculation mechanism to realize accuracy! Embodiments of the present invention will be described below with reference to the drawings.

In each figure, 1 is a servo-type positive displacement flowmeter main body, which is rotatably equipped with a desired rotor 2 and connected to a desired pipe line 3. Then, on the rotation axis of one rotor 2,
Reduction gear train 4. A servo motor 7 is connected via a magnetic joint 5 and a reduction gear train 6, and a feedback tacho generator 8 is attached to the servo motor 7, which is electrically connected to a servo amplifier S. However, for the amplifier 9, the tubes 10 and 11 for detecting the pressure before and after the rotor 2 of the flowmeter body 1 are connected to the conduit 3, and a slight difference is established between the two tubes 1G and 11. A pressure detector 12 is interposed so that a differential pressure electrical signal detected by the slight differential pressure detector 12 can be applied.

Therefore, by adding a signal corresponding to the differential pressure detected by the slight differential pressure detector 12 to the servo amplifier 9 and driving the servo motor T, a driving operation is performed to eliminate the differential pressure on the rotor 2. Therefore, the differential pressure before and after the rotor 2 can be reduced.

In addition, the other rotor 2 has a reduction gear train 13 on its rotating shaft, similar to the rotor 2 described above. A flow rate transmitter 16 is provided to which the Mli gear train 14 and the magnetic coupling 15 are connected, and can emit a pulse proportional to the flow rate from its final end.

Further, in parallel with the differential pressure detector 12, a differential pressure transformer 11 for correcting the amount of leakage is provided between the tubes 10 and 11.

By the way, in the embodiment shown in the first FXJ, a leakage correction calculator 18 is provided to receive the output signal from the differential pressure transformer 12゜11, and also to receive the output signal from the temperature needle TI provided before and after the rotor 2. .

The first embodiment shown in FIG. 2 has a calculation method slightly different from that of the previous embodiment, including temperature needles Tu, 'Lm and pressure gauge P.
Only the leakage amount is calculated through the leakage amount calculator 18 &, together with the physical correction amount by the micro differential pressure detector 12, and on the other hand,
A flow rate value obtained by rotating the rotor 2 is calculated by a measured quantity calculator 19 connected to a pulse t-16, and the obtained essence flow rate is obtained by adding both values by an adder 20. .

The action will be explained based on the above Iw formation.

When the fluid to be measured flows through the conduit 3, the rotor 2 is rotated by one rotation due to the transfer of the fluid, and the number of revolutions proportional to the flow rate is counted to obtain the flow rate.

In this case, as mentioned above, the servo motor T is connected to one side of the rotor 2 and applies driving force to the rotor 2 so as to reduce the differential pressure across the rotor 2 to zero. Main body 1
The measurement accuracy can be improved by gradually reducing the amount of leakage between the casing and the casing.

In this invention, since the relationship between the leakage lid and the differential pressure can be maintained in a proportional relationship, the slight differential pressure detector 11 constantly
By detecting the differential pressure after m, the leakage amount is calculated and counted together with the temperature and pressure correction factor by the leakage amount correction calculator 18, and the rotation speed proportional to the flow rate of the trochanter 2 obtained from the flow rate transmitter 16 is calculated. By calculating (addition or subtraction), the true value flow rate can be counted very easily.

According to this invention, in this servo type flowmeter, the differential pressure is detected separately from the servo mechanism, the amount of leakage before and after the rotor is measured, and the true flow rate is obtained by calculating the amount of leakage. Therefore, the servo control system and the high-accuracy calculation system can be made independent, which has the effect of improving measurement accuracy and stabilizing the yarn.

Furthermore, it is advantageous in terms of maintenance, and has the effect of always maintaining stable accuracy.

Furthermore, according to this invention, the differential pressure before and after the rotor is maintained in a proportional relationship with the leakage cap of the fluid passing between the rotor and the casing, so the leakage cap correction calculation based on differential pressure detection is extremely easy. It has features that can be obtained easily.

Further, according to the present invention, the target 11'i11! IfIIL
Even if the body has a large flow rate, the amount of leakage is proportional only to the differential pressure. Therefore, if a constant is determined based on the reference flow rate of a sonic nozzle, etc. in a low flow rate range, the relationship with a large flow rate can be expressed as ``11''.
Using this method, the true flow rate of high viscosity can be determined.

Furthermore, if the relationship between differential pressure and leakage amount is known, the discharge amount per rotor rotation can be calculated based on the rotor shape and housing.

It also has the effect of being able to determine the quintessence flow rate only by measuring the dimensions of the shape.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional servo-type positive displacement flowmeter, Figure 2 is a diagram showing the relationship between differential pressure and leakage amount in the present invention, and Figure 3 is a diagram showing the relationship between differential pressure and leakage amount in the present invention.
Wi and FIG. 4 are explanatory diagrams showing two examples of the sir 111 positive displacement flow needle according to the present invention. 1----------- Needle body 2--------
---Same trochanter 3-----, conduit 7--, servo motor 9-m...--1,--servo amplifier 12.17---minor difference Pressure detector 16---------Flow rate transmitter

Claims (1)

[Scope of Claims] ill In order to reduce the meter lid error, which is equivalent to the weight a, that occurs between the rotor and the casing due to the pressure difference that occurs before and after the rotor of a positive displacement flowmeter, the differential pressure is detected and an electric sensor is used. The pressure difference is reduced by converting and amplifying the servo motor, driving the servo motor, and transmitting the rotational force of the servo motor to the rotor, and integrating the flow signal as a pulse signal proportional to the rotation of the servo motor. In the servo-type positive displacement flowmeter, in order to further improve the accuracy of the servo-type positive displacement flowmeter, a volume proportional to the deviation pressure of the servo system is added to the flow rate signal as a correction signal. A servo-type positive displacement flowmeter. (21) The servo type fluid flow meter according to claim 1, wherein a differential pressure detector for calculation is arranged in parallel with a differential pressure detector for detecting a pressure difference in a servo system. (3) Differential pressure Claim 1, comprising a calculator that calculates a reference flow rate by inputting and calculating measured values such as inflow side pressure and inflow/outlet side temperature with respect to the detection signal and the flow rate signal of the servo-type positive displacement flowmeter. Servo-type positive displacement flowmeter described in Section 2 or Section 2 @